Evolution over time of the concentrations of 1 and 16 in non-irradiated libraries made from 1 and 2 (a) or 1 and 3 (b). The top halves of the graphs show the concentration of 1 (black squares) and 16 (red squares, in units of 1). The bottom halves of the graphs represent the oxidation (black circles) and replication (red circles) rates in the system, calculated by numerical differentiation of the curves in the top halves. Both libraries were prepared exactly as their equivalents in Fig. 4a,b, but they were kept in the dark.